University:
California State University, Northridge
Course:
COMP 440 | Database Design
Academic year:

2024
Views:

399

Pages:

10
Author:

Samuel K.

**Quiz: Advanced Data Modeling** **Due Oct 4 at 11:59pm** **Points 15** **Questions 15** **Time Limit 30 Minutes** **Allowed Attempts 2** **Take the Quiz Again** **Attempt History** **Attempt** | **Time** | **Score** ------------|----------|---------- LATEST | 24 minutes | 12 out of 15* * Some questions not yet graded **Score for this attempt: 12 out of 15** Submitted Oct 4 at 3:16pm This attempt took 24 minutes. **Question 1** 1 / 1 pts The relationships depicted within the specialization hierarchy are sometimes described in terms of "is-a" relationships. * True * False **Correct! The relationships depicted within the specialization hierarchy relationships can be described in terms of "is-a" relationships.** Question 2 1/1 pts What type of entity can have disjoint or overlapping entity subtypes. supertype Correct. Supertype can have disjoint and overlapping entity subtypes. specialization subtype extended Question 3 1/1 pts To model time-variant data, one must create a new entity in an M:N relationship with the original entity. True False Correct. Model time-variant data one must create a new entity in a 1:M relationship with the original entity. A 1:M relationship can be turned into a M:N.Question 4 1/1 pts A subtype contains attributes that are common to all of its supertypes. True False Correct. A supertype contains attributes that are common to all of its subtypes. Question 5 1/1 pts Using a data modeling point of view, what data refers to data whose values change over time and for which there must be kept a history of the data changes? history specialization relationship time-variant Correct. Time-variant data refers to data whose values change over time. Question 6 1/1 pts Which of the answers below can be used to implement relationships among entities? A code key A database kev A system key A foreign key Correct. Primary keys and foreign keys are used to implement relationships among entities. Database key, code key, and system key are not used to implement relationship among entities. Question 7 Not yet graded / 1 pts Define surrogate key and when to use it. Your Answer: A surrogate key is a primary key created by the database designer to simplify the identification of entity instances, and values for it can be generated by the DBMS. Surrogate keys are useful in the following situations: When there is no natural key When the selected candidate key has embedded semantic contents When the selected candidate key is too long